1. Field of the Invention
This invention relates to an apparatus for transferring a lithographic plate from a horizontal conveyor to an overhead conveyor in the course of transporting lithorgraphic plates used for printing newspaper and the like.
2. Prior Art
A lithographic plate of the kind used for printing newspapers and the like takes the form of a thin aluminium sheet having a thickness of the order of 0.3 mm and having one or both end regions thereof folded over to lie at approximately 30.degree. to the plane of the sheet. To transport the plates from one process station to another within the printing works, the plates are carried by horizontal and overhead conveyors and apparatus is provided for transferring the plates from the horizontal conveyor to the overhead conveyor.
A known apparatus for transferring a lithographic plate from a horizontal conveyor to an overhead conveyor is shown in FIG. 5 of the accompanying drawings. The form of the lithographic plate itself is illustrated in FIGS. 6 and 7, where a turned over end region of the plate S is indicated by the reference S1.
As indicated in FIG. 5, the lithographic plate S is conveyed longitudinally on a horizontal conveyor 30 from one process station and is delivered onto an input conveyor 30' at the input of an apparatus for transferring the lithographic plate to a selected one of a plurality of overhead conveyors 34. The input conveyor is intermittently operated in synchronism with pairs of opposed hooks (not shown) carried by a plate elevating means of the transferring apparatus in the form of a pair of spaced apart endless chains 40 arranged to be driven in both directions.
The input conveyor 30' feeds the lithographic plate S onto a rotatable orientating means 32 which orients the lithographic plate S for conveyance either by the left hand or right hand run of the elevating means 40. The plate S is then picked up by a pair of hooks on the chains engaging the turned over end portion S1 of the plate and the plate is conveyed upwardly supported on the hooks until the plate reaches a position slightly above a selected movable plate bed 44. While the plate is being conveyed upwardly from the orientating means 32, the plate bed 44 is located in a standby position indicated at A. Once the plate S has been conveyed to the position slightly above the plate bed 44, the plate bed is moved transversely of the chains 40 to the loading position indicated at B and the chains 40 are driven downwardly to deposit the lithographic plate onto the plate bed 44 which then moves to a transfer position C in which the upper end of the lithographic plate S is presented to an overhead conveyor 34 which picks the plate from the bed 44 and carries it towards another process station.
A known plate transferring apparatus as described above is complicated in construction because the plate bed 44 must be movable transversely of the conveying chains 40 and, in addition, the reciprocating motion of the chains 40 and the plate bed 44 causes the lithographic plates to swing, possibly resulting in an unstable transfer and restricting the reliability and handling capacity of the apparatus.